1. Field of the Invention
The present invention relates to an electronic device and a method for producing the same. In more detail, the present invention relates to an electronic device such as a semiconductor integrated circuit, a semiconductor device or a surface acoustic wave (SAW) device, and a method for producing the same.
2. Description of the Related Art
Various electronic devices comprise patterned electrodes or metallization on a substrate. For example, in the case of a surface acoustic wave device, an aluminum electrode is formed on a single crystal piezoelectric substrate by a reactive ion etching (RIE). More specifically, as shown in FIGS. 1A and 1B, a surface of an electrode film 2 provided on a single crystal piezoelectric substrate 1 is covered with a photoresist 3, and the electrode film 2 is selectively etched using a chlorine-based gas such as Cl2 or BCl3 and a patterned photoresist 3 as a mask. However, the electrode film 2 is not always completely removed and is sometimes left behind on the single crystal substrate 1 owing to heterogeneous distributions of the film thickness of the electrode film 2 or reactive ion etching rate on the surface of the single crystal substrate 1 as shown in FIG. 1A. A residue eliminating process called over-etching becomes therefore inevitable in order to completely remove the electrode film 2 without leaving any residue behind. As shown in FIG. 1B, an over-etching treatment by 5 to 50% excess of the overall etching time under the same etching condition is applied in the over-etching method, thereby slightly etching into the single crystal substrate 1.
However, the portions where the electrode film 2 has been removed and the single crystal substrate 1 has been exposed to chlorine plasma during the over-etching become exposed. Consequently, the single crystal substrate 1 is damaged, forming damaged layers 4 as shown in FIG. 2, thereby deteriorating characteristics of the acoustic surface wave device.
It has been a common view that the cause of the substrate damage due to over-etching as described above is a physical damage caused by impact of ions colliding with the substrate during the reactive-ion etching. Accordingly, the substrate damage due to ion irradiation has been suppressed by the following methods: (1) reducing the ion irradiation energy; (2) improving homogeneity of the ion etching rate; and (3) detecting the etching terminal point with high precision. However, it was impossible to completely inhibit the damage of the substrate by the conventional method, although it can be reduced.
The present invention is directed to a method that can solve the aforementioned problem and reduce the damage of the substrate by the reactive ion etching during production of an electronic device. The present invention is also directed to an electronic device prepared by the method and having a excellent device characteristics due to less substrate damage.
An electronic device comprises: a support selected form the group consisting of a single crystal substrate, single crystal film, triaxial orientation film or uniaxial orientation film; a lower electrode layer comprising a material capable of reactive-ion etching with a fluorine-based gas and formed on the support; and an upper electrode layer comprising a material capable of reactive-ion etching with a chlorine-based gas and formed on the lower electrode layer.
The method for manufacturing an electronic device, comprises the steps of: forming a base film comprising a material capable of reactive-ion etching with a fluorine-based gas, on e.g., either a single crystal substrate, single crystal film, triaxial orientation film or uniaxial orientation film; forming a thin film comprising a material capable of reactive-ion etching with a chlorine-based gas, on the base film; etching the thin film by reactive ion etching with a chlorine-based gas using a mask having a predetermined pattern; and etching the base film exposed by the etched thin film by a reactive ion etching with a gas containing the fluorine-based gas.
The base film or lower electrode layer preferably contains at least one element selected form the group consisting of Si, Mo, W, B, C, S and Ta and has a thickness of about 0.5 nm to 1000 nm. The support may comprise a piezoelectric material.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.